1. Field of the Invention
The present invention relates to a television broadcast receiver for receiving terrestrial broadcasts.
2. Description of the Related Art
Conventionally, directional antennas such as a Yagi antenna are used to receive terrestrial broadcasts. A directional antenna has a high directivity to be able to receive a weak radio wave or signal. At the same time, the directional antenna has a drawback that it can receive only a radio wave coming from one direction. This is not a big problem in countries like Japan where many broadcast towers are concentrated in one location. However, in countries like the United States of America, there are many areas where broadcast towers spread around cities. If a directional antenna such as a Yagi antenna is used in such case, it may occur that the directional antenna cannot receive many broadcasts from broadcast towers even if the directional antenna is placed close to the broadcast towers.
In order to solve such problem, the EIA (Electronic Industries Association)-909 standard “Antenna Control Interface” was instituted, which provides a technology that a television broadcast receiver can control and change receiving directions of the antenna. More specifically, it is a standard to connect, to a television broadcast receiver, a so-called smart antenna which is capable of changing its receiving directions, and to control the antenna by the television broadcast receiver via a modular terminal. In the present specification, the two kinds of antennas are distinguished by referring to the directional antenna, such as the Yagi antenna, as a unidirectional antenna, and by referring to the antenna, capable of changing its receiving directions, as a multi-directional antenna.
There is a possibility that a unidirectional antenna is connected to a television broadcast receiver, to which a multi-directional antenna should be connected. However, there is no known television broadcast receiver for receiving terrestrial broadcasts that allows a user to optionally select the kind of antenna connected to the television broadcast receiver, or that can properly switch antenna control modes depending on the kind of antenna connected to the television broadcast receiver. Thus, even if a unidirectional antenna is connected to a television broadcast receiver capable of controlling a multi-directional antenna, there is a possibility that the television broadcast receiver may perform a control operation for a multi-directional antenna, which is meaningless for the connected unidirectional antenna.
For example, some of such television broadcast receivers have an omni-directional scanning function to sequentially command all the receiving directions of a multi-directional antenna for an arbitrary channel selected by a user, and to automatically determine a receiving direction, which enables television broadcast signal reception in a best receiving condition for the channel, on the basis of e.g. signal intensities of a television broadcast signal of the channel in all the receiving directions. Such receiving direction to enable the best receiving condition is referred to as best receiving direction in the present specification.
This omni-directional scanning process is a completely unnecessary process for a unidirectional antenna, which is incapable of changing its receiving direction. The omni-directional scanning process, when performed for the unidirectional antenna, is a waste of time. Accordingly, it is necessary or desired to perform the omni-directional scanning process only in the case where the television broadcast receiver is connected to the multi-directional antenna.